I don't understand why they are franchising Dez and losing Murray to be honest. I'm sure it is a no brainer for everyone else because nobody seems to be debating it so I must be missing something. The way I see it Dez needs to be locked up because he is virtually the face of the franchise and since Romo is old-ish and injury prone they will need Dez to allow his eventual successor to have a chance. Murray seems like an obvious franchise tag candidate since getting him on a one year deal as a top 5 back is very team friendly since he is actually (IMO) the top 1 back, but he has a limited shelf life and an awesome scheme fit. So IDK. I guess if locking up Dez isn't feasible at the moment then what they are doing is the right move. I am far from a salary cap expert.
With that said, I suppose they can draft someone for a lot less than 9m. The dropoff in skill between Murray and Randle was palpable because Randle didn't run like a zone back, so that's the danger if they just try to fill Murray's spot with anyone. If they tried to replace him cheaply they would definitely need a committee because you need to replace his power running/vision, his pass catching and his pass blocking. Their offense might lose a bit of flexibility.
Speaking of Romo's eventual successor, this sounds weird but if the Jets draft someone I would love Dallas to grab Geno Smith. He plays quite a similar style to Romo, he is a massive immediate upgrade on Weeden and actually has the potential to be good in the right situation. But even with his strong end to the season I think he's likely to be a backup this year, unless he starts for 5 weeks while Mariota sits or something.